1. Field of the Invention
The present invention relates to an optical apparatus such as an interchangeable lens and an image pickup apparatus (camera), and particularly relates to an optical apparatus provided with an optical image shake correction function.
2. Description of the Related Art
Interchangeable lenses and image pickup apparatuses are often provided with an optical image shake correction function in which an image shake correction optical element such as a shift lens and a variable angle prism is driven to reduce image shake caused due to hand jiggling or the like. A high image shake correction effect of the optical image shake correction function is achieved by using a position detector that can detect a position of the image shake correction optical element with high accuracy.
As such a position detector, a relative position detector such as a pulse encoder having high position detection accuracy is widely used. However, the position detection by using the relative position detector requires accurate setting of an origin position which is a reference position for the position detection. In the optical image shake correction, a position is selected as the origin position which corresponds to an optical origin position allowing a light ray proceeding on an optical axis of an image pickup optical system to straightly progress without being refracted.
Methods for setting the origin position include one using an absolute position detector separate from the relative position detector. However, the use of the absolute position detector is not preferable in view of miniaturization and cost-lowering of the optical apparatus. Therefore, the following method has been proposed which sets the origin position by using only the relative position detector.
Japanese Patent Laid-Open No. 6-43518 discloses a method for setting the origin position which causes an image shake correction optical element to bring into contact with a mechanical end of a movable range (hereinafter referred to as “movable range end”) of the image shake correction optical element and detects the origin position by using a distance measured in advance from the movable range end to the origin position. Further, Japanese Patent Laid-Open No. 2007-101671 discloses another method for setting the origin position which detects movable range ends of an image shake correction optical element on its both sides and sets a center of the movable range ends as the origin position.
The optical apparatuses provided with the optical image shake correction function generally include a lock mechanism which mechanically locks movement of the image shake correction optical element in order to limit the movement thereof within a lock range near the origin position when the optical image shake correction function is not used.
However, an end face of the lock mechanism forming an end of the lock range may be abraded due to multiple switching between a locked state and a lock-released state (unlocked state). Such abrasion makes it impossible to accurately set the origin position merely by detecting the mechanical movable range end in the lock mechanism using the method disclosed in the Japanese Patent Laid-Open Nos. 6-43518 and 2007-101671. Inaccurate setting of the origin position makes it impossible to control the position of the image shake correction optical element to the origin position in the locked state, which may cause displacement of the image shake correction optical element from the origin position by a gap amount between the lock mechanism and the image shake correction optical element. Such displacement from the origin position causes color shift in a captured image or the like, which deteriorates optical performance of the optical apparatus.
A similar problem to that in the lock mechanism occurs in a case where the end face forming the end of the movable range of the image shake correction optical element is shifted from a default position by changes with time due to abrasion or the like.